The invention disclosed herein relates generally to actuators for rotational positioning of a member, and more particularly to an actuator design capable of employing a unidirectional motor to alternately position a rotating member against first and second fixed stops.
In certain actuator applications, such as for positioning closure members in fluid flow control devices, it is necessary or desirable to be able to alternately rotate the closure member to positions angularly separated by 90 degrees. It is further desirable to be able to accomplish this positioning with a unidirectional motor for which the power supply and control circuitry are generally simpler and less expensive than for a bidirectional motor. Further, in some applications, such as in automatic flue damper apparatus having a sheet metal flue section with a closure disk therein, it may be necessary or desirable to firmly position the closure disk against a fixed perimeter stop or seal regardless of normal tolerance variations of the sheet metal parts. This requires that the closure member be angularly repositioned in opposite directions to open and close the damper. Thus, a need exists for a simple low cost actuator capable of utilizing a unidirectional motor to rotate a closure member alternately in opposite directions to open and closed positions.